From: Dan Brickley <danbri@w3.org>
Subject: Re: MISC: Internet Media Type registration: proposed TAG finding
Date: Wed, 22 May 2002 23:50:57 -0400 (EDT)
> On 22 May 2002, Dan Connolly wrote:
>
> > > I ask
> > > that the WebOnt WG discuss whether to send a polite note back rejecting
> > > this interpretation of our work.
> >
> > I don't think we should.
>
> FWIW, Peter's dissatisfaction with my note (which wasn't addressed here)
> is noted.
>
> I continue to regard the WebOnt language (and the RDF 1.0 syntax, and it's
> MT, and RDFS) as a component of the wider Resource Description Framework,
> but don't propose we take time up discussing labels here.
Well then what is ``the wider Resource Description Framework''? There are
many reasons that it can't be RDF as it currently exists, ranging from the
sublime to the ridiculous.
On the sublime end, a number of people have been describing the problems
that result from trying to make RDF represent disjunctions, negation, and
classes. One either ends up having entailment be severely curtailed or
with paradoxes. RDF is just not adequate for the job of being the language
for the semantic web.
On the ridiculous end, the Semantic Web Layer Cake makes RDF be one of the
layers, with several non-RDF layers on top. I suppose you could argue that
everything on top of RDF is RDF because it depends on RDF. However, in
that case I'll just stop talking about RDF and use XML instead, because all
the semantic web layers are on top of the XML layer.
So, if you don't mean RDF as it exists right now, then why not use the
accepted name for this wider effort - the Semantic Web?
> (<onlyhalfjoking>We used to call this effort the Platform for Internet
> Content Selection; maybe we could go back to that name if folks really
> don't like the RDF TLA?</onlyhalfjoking>)
This is *no* joke to those of us who care about firm foundations for the
Semantic Web. We have been fighting against the view of RDF as the one
true language for quite some time now. I think that it is past time for
the proponents of RDF as the one true language for the Semantic Web to put
up or shut up. Either demonstrate that RDF can be used to correctly
represent disjunctions, negations, quanitifers, classes, etc., or stop
saying that RDF is the one language for the Semantic Web.
> [...]
>
> > A consumer of the above document either or does or doesn't grok
> > DAML+OIL semantics; it can come to more of the relevant conclusions
> > if it applies DAML+OIL axioms, but since everything is monotonic,
> > there's no harm done if it doesn't apply those axioms.
> >
> > This is the principle of partial understanding in action.
> > I have tried to make this point in the past...
> > http://lists.w3.org/Archives/Public/www-webont-wg/2002Mar/0339.html
> > but I'm not having much luck.
>
> How about we try to think about this issue in forward-looking rather than
> backward-looking terms?
>
> Given RDFS and WebOnt, we're looking at partial understanding in terms of
> RDFS-aware tools dealing with with WebOnt-enriched RDF Schemas (er,
> Ontologies). So how about we forget the past and look to the future?
>
> Imagine you're in the WebOnt v3.0 WG, looking back on the products of this
> group, balancing v3.0's backward compatibility with present-day
> requirements and opportunities. Presumably WebOnt v1.0 isn't the one true
> ontology language to end them all?
Agreed, but I'm not making any claims to the effect that OWL is the final
language for representing ontologies, and I'm certainly not making any
claims that OWL is suitable at all for representing full first-order
logic.
> We might expect a version 1.1 or 2.0 at
> least. Or perhaps people will take to describing their RDF Schemas and Web
> Ontology vocabularies using one of the various RDF-oriented rule
> languages. Maybe W3C will even do a REC-track spec or two for such a rule
> language. And what about datatyping? The XML Schema WG is still active,
> and might well produce refinements of the XML Schema datatyping system,
> which will at some point manifest itself in the RDF and Web Ontology
> world. The future looks busy.
Again agreed.
> Partial understanding in action: people will write tools to work with the
> WebOnt 1.0 language, just as they're writing tools to work with RDF Schema
> vocabulary descriptions now. We need to think about how these new WebOnt
> tools will, or won't, be suprised by documents that draw on features
> defined in specs subsequent to WebOnt 1.0. Is a WebOnt ontology that draws
> upon some additional (webont v2, rdf-rules-1.0?) namespace still really a
> WebOnt doc? Is it an RDF Schema for that matter? (re the latter, yes, imho).
Now here is where I think that you are getting into very deep waters. I do
not believe that it is necessarily the case that any future language has to
be viewed as OWL. Maybe OWL will evolve in a way that extends its
capabilities, so that ontologies in future versions of OWL will be
recognizable as ontologies in the current version of OWL. Maybe future
versions of OWL will not be backward compatible with the current version of
OWL. Maybe OWL will be considered to not be a reasonable language to
extend at all and ontologies will in the future be written in a different
language entirely I just don't know, and I don't think that anyone knows,
which way the future will pan out. What I do know, however, is that
stating that all future Semantic Web languages will be RDF is ridiculous.
> At the instance data level, all this shouldn't matter. (Thankfully, for
> the poor end users...)
How so? There is lots of instance information that doesn't fit into RDF.
Suppose I want to say that John's brother is either Jim or Joe. How can I
say that in RDF? Suppose I want to say that John loves everyone. How can
I say that in RDF?
> A question. Or maybe even test case...
>
> Is the following XML doc 'mere RDF', or a 'WebOnt instance document'? (or
> a DAML+OIL doc). What changes in the Web might change our answers to this
> question?
>
> <web:RDF xmlns:web="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
> xmlns:wn="http://xmlns.com/wordnet/1.6/" xmlns="http://xmlns.com/foaf/0.1/">
>
> <wn:Person>
> <name>Dan Brickley</name>
> <mbox web:resource="mailto:daniel.brickley@bristol.ac.uk"/>
> <mbox web:resource="mailto:danbri@w3.org"/>
> <homepage web:resource="http://purl.org/net/danbri/"/>
> <dateOfBirth>1972-01-09</dateOfBirth>
> <depiction web:resource="http://rdfweb.org/people/danbri/2000/01/01/Image1.gif"/>
> </wn:Person>
>
> </web:RDF>
The above is, of course, RDF.
How about the following?
<web:FOL xmlns:web="http://www.w3.org/[semanticweb]"
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
xmlns:fol="http://www.w3.org/[fol]"
xmlns:finance="http://[finance]">
<fol:disjunction>
<fol:disjunct>
<finance:monetaryobligation>
<finance:from rdf:resource="DanBrickley" />
<finance:to rdf:resource="PeterPatel-Schneider" />
<finance:amountinbritishpounds>1000000</finance:amountinbritishpounds
</finance:monetaryobligation>
</fol:disjunct>
<fol:disjunct>
<finance:financialinstitution rdf:resource="finance:bankofengland" />
</fol:disjunct>
</fol:disjunction>
</web:FOL>
Is this RDF? If so, where is my million pounds?
> Note that currently the RDF schema at the http://xmlns.com/foaf/0.1/
> namespace asserts that the 'mbox' property used here is a
> daml:UnambiguousProperty. At some point it'll probably use WebOnt 1.0
> vocab instead. And eventually I'll use whatever ontology, rules and schema
> language best capture the intended meaning of the classes and properties
> in my namespace. Maybe I won't change the document you get at the
> namespace; I might send digitally signed RDF to a usenet group instead.
> But the intention should be clear: describe the vocabulary as accurately
> as possible with the machinery currently to hand.
Well I argue that this RDF schema is either broken, in that it doesn't mean
what it is supposed to mean, or it is not an RDF schema. I view what you
are trying to do as the same as me thinking that if I watch enough
videotape of Tiger Woods playing golf, I will be able to play golf just as
well as he can. Mentioning tokens does not imply understanding them, nor
does it imply being able to use them in the way they are supposed to be
used.
> Dan
Just to make the above perfectly clear, I view your view of RDF and the
Semantic Web as misinformed and, moreover, dangerous.
Peter F. Patel-Schneider
Bell Labs Research